The wireless communication industry is characterized by rapid growth in demand for services under constraints on the amount of licensed radio frequency spectrum available. These conditions have served as an impetus for users to be as spectrum efficient as advances in the state of the technology allow. Cellular radio is a prominent example of a spectrum-efficient design in which low power base stations reuse the same sets of radio channels hundreds or thousands of times (e.g. for thousands of simultaneous phone calls) within a given geographic area. Digital radio is an additional improvement that allows each radio channel or frequency band to carry more information compared to the same spectrum used in older “analog” radio designs. Cellular radio, digital radio and other advancements have resulted in greater traffic capacity and the ability of wireless communications companies to serve more customers within the prevailing spectrum constraints.
Even with aggressive infrastructure deployment and improvements in technology, however, demand for wireless services has exceeded available capacity in areas with the highest customer concentrations. Limits on the availability of additional licensed spectrum are a binding constraint in need of relaxation and supplementation to allow further growth. In response, the Federal Communications Commission (FCC), at the direction of the United States Congress, continues to aggressively auction additional spectrum to the highest bidder, subject to its auction rules and conditions. The spectrum auctions generate revenue for the United States Treasury while transferring spectrum licenses to those who (in theory) place the highest value on the spectrum.
Unfortunately, the auctioned-and-transferred spectrum often has existing, incumbent users that must be moved to other spectrum or induced to cease operations before the auction winner can effectively use the newly purchased spectrum. Further, the law often protects incumbent users from radio interference from new licensees.
As an example, consider FIG. 1 which illustrates the planned auction of UHF spectrum in the 700 MHz band. The FCC's strict regulatory stance on protecting incumbent television stations in the Ultra High Frequency (UHF) band provides a case-in-point that illustrates the need for the invention described herein. The UHF bands in the 747–762 and 777–792 MHz ranges were originally licensed for UHF television broadcast services. The 747–762 MHz band includes television channels 60, 61 and 62, whereas the 777–792 MHz band includes television channels 65, 66 and 67 (see FIG. 1). A number of stations are operating on these channels and/or adjacent channels, particularly in or around certain major metropolitan areas, however, many large regions of the country do not receive any broadcasts on these channels (see maps shown in FIGS. 2A to 2J).
FCC Auction #31 for the 747–762 and 777–792 MHz bands is scheduled to begin on Mar. 6, 2001. The auction was postponed as several potential bidders publicly requested that Congress and the FCC delay the auction while the FCC considers better ways to resolve the spectrum encumbrances and other important matters. Additional spectrum, including encumbered spectrum in the 700 MHz band and in other bands, is slated to be made available in the future.
The presence of high power television broadcast signals generally serves as a technical impediment or is technically mutually exclusive to the other highly valued uses (e.g. wireless communications) intended by the auction winners and, indeed, by the FCC itself. Many planned wireless services that might utilize this band would be subject to severe interference from such television signals. Similarly, the operation of the new wireless communication services on such bands, in close geographic proximity to the television stations and their customers, would interfere with reception of the television broadcast signals.
The FCC, however, ordered the auction of these portions of the UHF-TV band without first clearing the band of incumbent television broadcasters. In fact, for many years to come, the relevant law protects the television broadcasters from harmful interference from new licensees. The FCC's long-term plan is designed to encourage the migration of all television broadcasters to other spectrum reserved for digital television (DTV). Their plan calls for television broadcast stations to convert from analog transmission to DTV transmission and to move to the DTV channels by 2006; provided that the market penetration of DTV receivers achieves high enough levels (defined as approximately 85 percent in major markets) by 2006. If the FCC's stated DTV household penetration is not achieved, however, it is conceivable that incumbent television broadcasters could remain on their present channels (and/or simulcast) until much later, perhaps until 2014. These uncertainties and delays are daunting problems for auction winners who may need to invest heavily to acquire the spectrum and may need to use it immediately to meet customer demands.
Hence a need exists for a technique to allow increasing use of spectrum by new wireless communication services in the presence of existing broadcast stations that may be on the same or adjacent channels. A need exists to allow nearly concurrent use in increasing geographic areas that encroach on existing users, while mitigating interference problems.